1. Field of the Invention
Embodiments of the present invention relate to signal processing. More particularly, embodiments of the invention involve a system and method for estimating a symbol rate of a signal that does not require prior knowledge of the signal's structure and is accurate in the presence of frequency offset and noise.
2. Description of Prior Art
Signal modulation is the process of encoding a signal with information—such as voice, data, or an image—on a carrier signal, and demodulation is the process of recovering the information from the carrier signal at a signal receiver. Various modulation schemes are known, including amplitude modulation, frequency modulation, and phase modulation. In each modulation scheme, a given state of the carrier signal representing one or more bits of data is commonly referred to as a “symbol.”
By way of example, phase modulation, commonly referred to as phase shift keying (PSK) in digital terminology, involves encoding information on the carrier signal by changing the phase of the signal. Each phase possibility is a symbol. For example, binary phase shift keying uses two symbols, each presenting one bit of data, and quadrature phase shift keying uses four symbols, each presenting two bits of data.
It is often desirable to determine a symbol rate of a signal, or the frequency at which symbols are transmitted in the signal. It may be desirable to determine a symbol rate, for example, to characterize an unknown signal detected in a surveillance situation.
Known methods of symbol rate estimation include the “Non-data Aided Maximum Likelihood Based” algorithm as well as the “Oerder and Meyr” algorithm. Unfortunately, these methods suffer from various problems and limitations. For example, such methods require the user to know certain parameters of the signal to be analyzed, such as the shape of signal pulses. Thus, in situations where very little or nothing is known about the signal to be analyzed, existing methods of symbol rate estimation are of no use. Furthermore, the presence of signal noise and frequency offset can impede symbol rate estimation using the known techniques.
Accordingly, there is a need for an improved aircraft engine thrust reverser that does not suffer from the problems and limitations of the prior art.